L-929 cells harboring ectopically expressed RelA resist curcumin-induced apoptosis

Curcumin (diferuloyl methane), the yellow pigment in turmeric (Curcuma longa), is a potent chemopreventive agent. Curcumin induces apoptosis of several, but not all, cancer cells. Many cancer cells protect themselves against apoptosis by activating nuclear factor-kappaB (NF-kappaB)/Rel, a transcription factor that helps in cell survival. Signal-induced activation of NF-kappaB is known to be inhibited by curcumin. To understand the role of NF-kappaB in curcumin-induced apoptosis, we stably transfected relA gene encoding the p65/RelA subunit of NF-kappaB, into l-929 cells (mouse fibrosarcoma) and the relA-transfected cells were resistant to varying doses of curcumin (10(-6)-10(-4) m), whereas the parental cells underwent apoptosis in a time- and dose-dependent manner. The relA-transfected cells showed constitutive NF-kappaB DNA binding activity that could not be inhibited by curcumin and did not show nuclear condensation and DNA fragmentation upon treatment with curcumin. When a super-repressor form of IkappaB-alpha (known to inhibit NF-kappaB) was transfected transiently into relA-transfected cells, the cells were no longer resistant to curcumin. Our results highlight a critical anti-apoptotic role for NF-kappaB in curcumin-induced apoptosis.